I have just completed Campaign on Challenging: 137619
This was my first play through. Started on patch 1.04 and finished on 1.05.
Never used more than one Titan (Warhound) in my Core, thereby suffered some heavy loses all the time and did not have requisition points to fill out all available unit slots (Had 12 of them not filled in the final battle ).
Shadowswords (with weapon upgrade), Land Riders (Achilles modification) and close combat Dreadnoughts made the game for me.
Surprisingly, space marine snipers and Centurions with heavy bolters were the most useful troopers in the last missions.